Question

Write as a simplified single angle expressions of either sine or cosine. cos(pi/7)cos(pi/5)-sin(pi/7)sin(pi/5)

Answer 1

this is the addition angle formula for cosine

Answer 2

so your job is to add up
\[\frac{\pi}{7}+\frac{\pi}{5}\]

Answer 3

Do I have to get common denominators before I add or is the answer 2pi/35?

Answer 4

@satellite73?

Answer 5

anyone??

Answer 6

the answer is cos(12pi/35)

Answer 7

use this formula
cos(A+B) = cosAcosB - sinAsinB

Answer 8

@niksva do you mean cos(2pi/35)? if it is cos(12pi/35) how did you get that answer?

Answer 9

cos(pi/7 + pi/5) = cos(5pi+7pi/35 )
= cos(12pi/35)

Answer 10

@niksva Thank You!!!!!!